1. Field of the invention
The invention concerns a paper machine for the production of tissue paper.
2. Discussion of the Related Art
Reference is made to DE 31 12 070 A1.
As known, tissue paper is normally produced in a fashion such that the web is formed on a relatively short wire section resembling a four-drinier wire, where the headbox applies the fiber suspension on the wire in the region of a breast roll which frequently is open or provided with an inner vacuum, where the web--for backing by the wire--runs past conventional dewatering elements, for instance register rolls, deflectors, foil slats, suction boxes and a suction roll, of which each withdraws water from the fiber web. At the end of the wire section, the web transfers onto a so-called pick-up felt, with the aid of which it proceeds for further drying to the press section and drying section.
With the dual wire machine customary nowadays, the stock is injected as a machine-wide jet from the headbox nozzle into the wedge-shaped entrance gap between the two wires. It runs then, between the wires, around the shell of the forming cylinder and, as a still moist web, is then carried off by one of the wires. A press felt, or also pick-up felt, then picks the web up off the wire. The press section consists again of usual presses provided with two press rolls and a press felt, or a large-diameter tissue cylinder (Yankee cylinder) is used as one of the two press rolls.
With these prior tissue paper machines, a considerable disadvantage is constituted by the fact that the tissue web, in the press section, always clings to the press felt, whereby a strong tendency of remoistening the tissue web by this press felt is given, and the drying of the tissue web is thus considerably impeded, so that more press cylinders than necessary are being used.
The problem underlying the invention consists in achieving an overall arrangement of a tissue paper machine such that, for one, a remoistening of the tissue web will be avoided and, for another, a tissue machine design will be found which requires as few press units as possible.
The prevailing opinion in selecting suitable drying presses in contingence on the web thickness so far has been that for drying thin webs there are only simple roll presses suited which generate a sufficiently high contact pressure for a short time, thus optimally removing the water from a thin web (tissue web) due to the short path, whereas shoe type presses are suited essentially for drying thick, heavy webs, since they generate a persistent pressure which allows the water sufficient time for the considerably longer path in leaving the web.